The present invention relates to a solid electrolyte fuel cell configuration comprising metallic interconnect elements to act as fuel and oxidant manifolds and distribution channels.
In a fuel cell, oxidant and fuel are electrochemically reacted without burning to produce electricity directly. The reactants are supplied to the cell through manifolds and flow fields that direct reactants to the appropriate sides of a solid ceramic membrane, that membrane that acts as an electrolyte. The membrane is coated with electrodes on both sides, and is impervious to the transfer of electrons, but not ions of the oxidant. Thus the streams of reactants are kept separate, but the electrons and ions from the reactants are allowed contact to effect the reaction. During operation electrons are emitted at the fuel side electrode of the solid electrolyte membrane whereas electrons are absorbed at the oxygen side electrode thereby generating a potential difference between the two electrodes. The solid electrolyte membrane separates the reactants; it transfers the charge in the form of ions and, at the same time, prevents an electron short circuit between the two electrodes of the solid electrolyte. For this purpose, the solid electrolyte membrane needs to have a low conductivity for electrons but at the same time, a high conductivity for ions through the vertical cross section of the membrane.
Solid oxide fuel cells typically operate at high temperature, often in excess of 600° C. This limits the selection of materials available for use as an interconnect that are able to withstand this temperature, and to simultaneously withstand an oxidizing environment on one side of the interconnect, and a partial reducing environment on the other. The material is also required to simultaneously maintain good electrical conductivity to collect the current generated by the cells. Most prior art interconnects have used ceramic materials and composites, however these materials demonstrate inferior electrical conductivity as compared to metals, and typically are not successful in withstanding both oxidizing and reducing environments simultaneously.
Ceramic materials also are expensive to purchase as raw materials, require moulding or other processing, and then firing or sintering. These steps are all labour intensive and require significant amounts of time to process. In addition, fine tolerances that are required in a solid oxide fuel cell stack are difficult to maintain when a green ceramic is sintered at the high temperatures required. Further, ceramic materials are brittle, and there can be significant losses during production due to handling and processing damage that occurs in the manufacture of the interconnect. Ceramic materials are also vibration and shock intolerant, which makes them unsuitable for applications where these factors are present, such as in automobiles.
Metallic interconnects which are machined from solid metal plates are known but are difficult to manufacture and as a result are expensive. There have been attempts to form metallic interconnects by bonding stacked metal plates together however such attempts have not been successful because of leaks forming between the metal plates and their inability to withstand the operating temperatures of solid oxide fuel cells. For example, U.S. Pat. No. 3,484,298 discloses a laminated electrode backing plate which is laminated using adhesives or other bonding agents.
Accordingly, it is a object of the present invention to disclose a metallic interconnect that can overcome the disadvantages of the prior art, and can be produced at a lower cost with finer more consistent tolerances, while being more robust and substantially leak-free.